For reasons I'm not going to try bother explaining, I've been handed a Nuendo session that I need to convert to a Logic Pro session for someone else. I'm doing that via OMF but that's not really important to the query.

Anyway, the Nuendo session has tracks in it which were recorded using overlapping 'takes' - ie, the ol' 'stacked waveforms' thing. Screenshot attached in case I'm not clear.

Is there a quick way to expand all of these to their own tracks? The guy with Logic needs access to everything... or does it have to be done manually with creating new tracks and moving them?

When activating "lanes", they should "open up" in different lanes.
Then right click on the track header and choose "create tarcks from lanes"
See screenshot.

This should allow you to export all taks in tracks.

If the tracks don't "open up" in lanes, but are stacked on the same lane, then it's because the person who gave you the project, has manually stacked them one upon the other. In this case, all you can do is to drag them into individual lanes and then perform the above procedure.